Vaporisation was an execution method provided for by law on Gallifrey.
It was performed in a vaporisation chamber.
It was applied for the murder of the Lord President. For example, the Fourth Doctor, framed by the Master for the death of the President, was threatened by this kind of death sentence. (TV: The Deadly Assassin)
Similar techniques
By the time of Borusa's presidency, ordinarily it wasn't made provision for executions, except for severe cases threatening collective security, in which molecular dispersal was the employed method. (TV: Arc of Infinity)